Engine starting method and device

Abstract

An engine starting method for starting an engine by causing first fuel injection when a crankshaft is reversely rotated by a predetermined angle at the start, and then rotating the crankshaft forward to perform first ignition, the method comprising the steps of immediately stopping driving of a starter motor when a starter switch is turned off before the first fuel injection at the start; and continuously driving the starter motor forward until a cylinder into which an air / fuel mixture is supplied by the first fuel injection performs at least one exhaust stroke and then stopping the driving of the starter motor when the starter switch is turned off after the first fuel injection at the start.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates to an engine starting method for starting an engine comprising a starter motor, and an engine starting device used for implementing the method.PRIOR ART OF THE INVENTION[0002]Generally, when an engine is stopped, a compression load in a compression stroke of the engine acts as a brake in the process of inertial rotation of a crankshaft, the rotation once stops in the process of a piston in any of cylinders moving up toward a top dead center of the compression stroke, and then the piston is pushed back and stopped near a bottom dead center in many cases. Thus, in starting the engine, the crankshaft is rotated from the state where the piston in any of the cylinders is positioned near the bottom dead center of the compression stroke.[0003]When the crankshaft is rotated forward for starting the engine in this position, the compression load of the compression stroke is applied to the crankshaft immediately after the star...

AI Technical Summary

Benefits of technology

[0016]The present invention has an object to provide an engine starting method and an engine starting device that can prevent a reduction in startability of an engine when a starter switch is turned on and then immediately turned off.

[0020]If the starter switch is turned off after the first fuel injection as described above, the fuel is accumulated in the cylinder, which generates too concentrated an air / fuel mixture when the starter switch is next turned on and reduces startability of the engine.

[0022]As described above, when the starter switch is turned off after the first fuel injection, the driving of the starter motor is not immediately stopped but the starter motor is continuously driven until the cylinder into which the air / fuel mixture is supplied by the first fuel injection performs at least one exhaust stroke and then stopped. This prevents fuel from being accumulated in the cylinder, and thus prevents the inside of the cylinder from becoming wet with the fuel to make the next start of the engine difficult.

[0025]When the engine is started at extremely low temperature, the sum of compression torque and friction torque exceeds output torque of the starter motor in the compression stroke and the crankshaft stops in some cases. At this time, if the starter motor is continuously driven forward, the piston of the engine can be slowly displaced toward the top dead center of the compression stroke with gradual reduction in the compression torque by a compression leak in the cylinder of the engine, and the starter motor can accelerate the crankshaft after the compression torque exceeds a maximum value to complete the compression stroke. At this time, the air / fuel mixture is compressed in the cylinder, and thus the ignition operation is successively performed to perform an expansion stroke, and the crankshaft can be sharply accelerated to start the engine.

[0028]According to the present invention, when the starter motor is reversely driven and the starter switch is turned off after the first fuel injection, the driving of the starter motor is not immediately stopped but the starter motor is continuously driven during a set delay time and then stopped. This prevents fuel from being accumulated in the cylinder, and thus prevents the inside of the cylinder from becoming wet with the fuel to make the next start of the engine difficult.

Problems solved by technology

Particularly, when a rotor of the starter motor is directly connected to the crankshaft such as when a generator having a rotor directly connected to a crankshaft is used as a starter motor at the start of an engine, motor torque cannot be increased by a reduction mechanism, which requires use of a large expensive motor.

When the starter motor is used as the generator after the start of the engine, using a motor with high driving torque excessively increases inertia of the rotor because of a large mass thereof, thereby reducing response of the engine.

Startability and the response of the engine are in a trade-off relationship, and improvement in both thereof is difficult.

The engine is difficult to start under the extremely low temperature environments as described above because an increase in viscosity of engine oil or the like caused by a reduction in temperature suddenly increases torque (friction torque) applied to the crankshaft by sliding friction of a movable portion of the engine to excessively increase the maximum load torque (the sum of the compression torque and the friction torque) applied to the crankshaft in the compression stroke.

Specifically, under the extremely low temperature environments, the friction torque of the engine is considerable to extremely increase the maximum load torque applied to the starter motor in the compression stroke, and thus the engine cannot be started using the starter motor that outputs low torque.

It has been revealed that in the case where after the starter switch is turned on, the starter motor is reversely driven for once reversely rotating the crankshaft, the first fuel injection is performed when the crank angle position reaches a predetermined position, then the starter motor is driven forward, and the first ignition is performed when the crank angle position reaches the position suitable for performing the first ignition, the following problems occur when a driver once turns on the starter switch and then turns off the starter switch by misconstruing that the engine does not operate because of too quiet starting noise of the engine or the like.

Specifically, if the starter switch is turned off after the first fuel injection, fuel is accumulated in the cylinder with the starter motor being stopped, which generates too concentrated an air / fuel mixture when the starter switch is next turned on and reduces startability of the engine.

When an operation of turning on the starter switch and an operation of turning off the starter switch after the first fuel injection are repeated, the inside of the cylinder becomes excessively wet with fuel, which makes it difficult to start the engine.

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